An application starts with identity, income and expenses. Lenders verify income through recent payslips if you're salaried, or IR3 returns and business accounts if you work for yourself. Three months of bank statements is close to universal, because responsible-lending obligations require the lender to satisfy itself that the repayments are genuinely affordable alongside what you already spend.
The credit check pulls a report from Centrix, Equifax or Experian. It shows past credit accounts, any defaults or arrears, and, because New Zealand uses positive reporting, your history of on-time payments as well. A thin file isn't the same as a bad one. It just gives the lender less to read, which is why deposit size and steady income carry more weight for first-time borrowers.
The lender then folds the credit report, the verified income and the expense picture into one affordability assessment. That is where your rate and your loan size actually take shape. A clean record with a stable job and a deposit tends to land at the lower end of a lender's range. A patchy record or a stretched budget pushes the rate up, the loan size down, or both.